Typical roofing membrane compositions contain 100 parts of ethylene-propylene-diene terpolymer rubber, 100 parts of carbon black, and 50 parts of paraffin oil. The composition is either calendered or extruded into a membrane and then cured at high temperatures using conventional vulcanization techniques, e.g., by wrapping the calendered sheets of roofing membrane continuously on drums and curing the sheets with steam.
Prior to vulcanization, rubber compositions are usually soft and deform readily during handling. Consequently, rubber compositions, which are not vulcanized, are not useful as roofing membranes. The vulcanization step adds, of course, to the cost of the roofing membrane.